This is actually really fun to play with my friend groups. It could do with some ironing out the parts that occasionally act up or are unfair - e.g. there's a "don't move" challenge that you'll fail instantly if you happened to already be moving before the instruction appeared, which you most likely will be because you're probably not just standing still between challenges, and I'd say at least once a game there's some instance of one of us getting told we've failed or passed one despite blatantly not doing so. That aside, especially for a free game it has good variety to keep your interest and make sure it doesn't stagnate, and rounds are fast-paced so you're almost always moving and doing something. Games are also a good length - it's pretty addictive, so we'll almost always say "one more round", get to the end, and then end up playing more and more because, well, the next one is starting anyway and that one was short, so we might as well, and now the next one is starting, rinse and repeat.

Some gameplay elements can take some getting used to - I and a few friends found the strafe-jumping to be a pain in the ass to control at first - but it's pretty simple once you get accustomed.

Not sure what it would be like playing with strangers, but half the fun for me comes from the voice chat and jokes with friends while playing so I'd guess there's less enjoyment playing that way.